Method for improving the operational reliabilty of dosing devices

ABSTRACT

The dispensing of sample liquids is performed, particularly in case of high-throughput screening, by means of automatic dosing devices. Between individual dosing processes, the standstill of the dosing device may lead to an outgassing of the sample liquid existing in the dosing device, and to crystallization. In order to improve the operational safety, it is provided according to the method of the invention that a stand-by routine is initiated after termination of a dosing process. In the stand-by routine, liquid is dispensed via a dosing orifice of the dosing device. The dispensing step is repeated after a predetermined period of time.

The invention relates to a method for improving the operational safetyof dosing devices for chemical and/or biological liquids.

In modern testing methods, chemical and/or biological liquids providedfor testing are supplied, by means of automatic dosing devices, e.g. tosample supports. Using suitable dosing devices, the corresponding sampleliquids will be either dispensed or pipetted. In case of dispensing, thedosing device comprises a supply container accommodating the sampleliquid to be dispensed. The supply of the required quantity of sampleliquid to a sample support is performed, e.g. by use of a micropump, viaa dispensing tip. In case of pipetting, the sample liquid is firstsucked into the pipette by a pipetting tip and a micropump connectedthereto, and subsequently the sample liquid is dispensed onto the samplesupport. For this purpose, automatic pipetting devices have a processliquid provided within the pipetting device, and the receiving anddispensing of the sample liquid is carried out by correspondingreciprocating movements of the process liquid.

Automatic dosing devices are used particularly in high-throughputscreening. High-throughput screening processes are used for testing alarge number of chemical and/or biological samples in rapidchronological succession. In high-throughput screening, the chemicaland/or biological sample liquids are filled e.g. into deepened portions(wells) of titration plates. Known titration plates comprise e.g. 1536or 2080 wells. Depending on the respective design, the wells have avolume of less than 20 μl, particularly less than 5 μl. Thus, there willbe involved extremely small quantities of sample liquid which have to besupplied exactly to a respective well. The supplying of sample liquid isperformed e.g. by dispensing microdroplets by means of the dosingdevice. For this purpose, known dosing devices are provided e.g. withelectronically controlled micropumps. For generating suitably smalldroplets, of which the volume can be smaller than 1 nl and particularlysmaller than 0.5 nl, the channel of the pipetting or dosing device has adiameter of 10-100 μm and preferably 40-60 μm.

After termination of the dosing process, which can encompass e.g. thefilling of several titration plates, the dosing device will frequentlynot be required anymore over a longer period of time. Already after astandstill period of 15 minutes or less, depending on the sample orprocess liquid used, an outgassing of the liquid may occur. This causesa development of small gas bubbles internally of the dosing device.These bubbles will increase over time. Further, extended standstillperiods may result in crystallization or sedimentation of particles orcomponents contained in the sample and/or process liquid. These canlikewise increase over time. Such gas inclusions and/or crystallizationsor sedimentations may result in malfunction or clogging of the dosingdevice. Thus, prior to using the dosing device for a new dosing process,this device must always be cleansed. Such a cleansing process in whichboth the gas inclusions and the crystallizations or sedimentations mustbe completely removed, is massively time-consuming. Further, suchcleansing processes cannot be performed automatically since it has to beverified by user intervention that all depositions or gas inclusionshave been removed.

Even small gas inclusions or slight crystallizations or depositions maycause an impairment of an automated dosing process. Particularly inhigh-throughput screening, an exact quantity of sample liquid has to besupplied to each well of a sample support. The quantity of liquiddispensed by a dosing device is determined by the number of dropssupplied to a well. Thus, the drop volume has to remain constant and hasto be known during the whole dosing process. Already small inclusions ofair as well as slight depositions within the dosing device willadulterate the drop volume. This entails the effect that, during thenext dosing process, the volume of sample liquid supplied to the wellsof the sample support will be too small or too large. Thus, it isrequired that the drop volume be newly determined each time before a newdosing process is carried out. The determination of the drop volume isvery time-consuming. It has to be performed manually by the user.

It is an object of the invention to improve the operational safety ofdosing devices, and particularly to reduce the danger of outgassing,crystallization and depositions in dosing devices and/or the like duringstandstill times.

The above object is achieved by a method according to claim 1.

In the inventive method for improving the operational safety of dosingdevices for chemical and/or biological liquids, a stand-by routine isinitiated after termination of a dosing process. A dosing process isunderstood as the filing of wells of one or a plurality of titrationplates with sample liquid, e.g. in high-throughput screening. Theinvention provides that afterwards, within the stand-by routine, liquidis dispensed through a dosing orifice of the dosing device. If thedosing device is e.g. a dispensing or pipetting device, the dispensingof the liquid is performed through the orifices of the pipetting ordispensing tip. According to the invention, the dispensing of liquid isrepeated after a predetermined period of time. Preferably, in theinvention, such repeated dispensing of liquid is performed during thewhole standstill period at regular or irregular intervals.

Thus, in the method of the invention, it is provided that during thestandstill periods of the dosing device, a certain amount of liquid willbe dispensed by the dosing device from time to time. By the dispensingof liquid and the associated movement of the liquid, an outgassing ofthe liquid as well as an intrusion of gas through the dosing orifice isprevented or at least considerably reduced. At the same time, themovement of the liquid prevents or considerably reduces a crystallizingof the liquid or a deposition of particles or components. As a result,the dosing device will be directly ready for use even after extendedstandstill periods which can last up to several hours. The need for abothersome cleansing of the dosing device is obviated. Particularly,since the inventive method precludes disturbing gas inclusions ordepositions, it is not necessary anymore to newly determine the dropvolume prior to starting a new dosing process.

The liquid is preferably dispensed in the form of droplets. Thus, alsoduring the stand-by routine, the generated droplets will advantageouslyhave the preset drop volume. Thereby, it is safeguarded with increasedreliability that the drop volume does not undergo changes during thestand-by routine. In the process, a plurality of droplets, particularlymore than twenty, preferably more than fifty and most preferably morethan eighty droplets, are dispensed per liquid dispensing step. Thedispensing of a plurality of droplets safeguards a sufficient movementof the liquid within the dosing device. Further, gases which between twoliquid dispensing steps may have intruded into the device through thedosing orifice, will be reliably discharged again.

Further, it is rendered possible, in a liquid dispensing step, to have apredetermined quantity of liquid dispensed continuously. By thecontinuous dispensing of a predetermined quantity of liquid, the dosingdevice is subjected to a rinsing process. The rinsing will have theeffect that e.g. smaller depositions are detached or washed out from thedosing device. The quantity of liquid dispensed by the dosing device ina rinsing step is preferably in the range from 1 μl to 1 ml. Further,during the rinsing, the pressure is distinctly higher than during thedispensing of droplets.

According to an especially preferred embodiment, there is performed acombination of droplet dispensing steps, i.e. liquid dispensing steps inwhich droplets are dispensed, and rinsing steps, i.e. liquid dispensingsteps in which a continuous dispensing of liquid is carried out over apredetermined period of time. In this manner, both of the two abovedescribed advantages are realized. Preferably, between two rinsingsteps, a plurality of droplet dispensing steps are provided. This hasthe advantage that the overall quantity of liquid required during astand-by routine under maintenance of the operational safety is merelysmall, since only a small quantity of liquid is dispensed in the dropletdispensing step. By the provision of rinsing steps, it is furtherguaranteed that depositions and the like which possibly might begenerated in spite of the droplet dispensing steps, will be washed out.Preferably, more than ten, particularly more than twenty and mostpreferably more than fifty droplet dispensing steps are performed.

Tests have shown that a time interval from 20 to 80 seconds,particularly from 30 to 50 seconds, between two successive liquiddispensing steps, particularly droplet dispensing steps, isadvantageous. Rinsing steps are preferably performed every 30 to 90minutes. In this regard, the optimum time interval between successiveliquid dispensing steps depends on the liquid contained in the dosingdevice and also, e.g., on the order of rinsing steps and dropletdispensing steps. Further, in this regard, influential factors such asambient temperature, humidity of the ambient air and the like can beconsidered.

Preferably, if the dosing device is a dispensing device, the liquiddispensed in the droplet dispensing step is a sample liquid. This offersthe advantage that the stand-by routine can be interrupted at anydesired time and that the wells or the like can be filled immediatelyafter the interruption. If the droplet dispensing step is performed witha different liquid, e.g. a cleansing liquid, it has to be verified priorthe start of the next dosing process that the dosing device has sampleliquid and no cleansing liquid arranged therein near the dispensingorifice. Nonetheless, since sample liquids are very expensive, it may beof advantage to use a cleansing liquid or the like during the stand-byroutine.

The rinsing liquid will preferably be not the sample liquid but acleansing liquid or the like since the sample liquid is expensive andthe rinsing steps involve the dispensing of a relatively large quantityof liquid through the dosing device. In pipetting devices, preferred useis made of a process liquid for carrying out a rinsing step. A processliquid is used particularly in pipetting devices. This is a liquidcontained internally of the pipetting device and is utilized forgenerating a vacuum, e.g. by means of a pump, for sectional intake ofsample liquid. The use of a process liquid in pipetting devices isadvantageous in that only a small quantity of sample liquid has to besucked in. Thus, it is not required to fill the whole pipetting devicewith sample liquid. Thus, for instance, there will always exist processliquid in the region of the micropump. The process liquid is merelysucked into the pipetting tip and dispensed again therefrom.

The triggering of the stand-by routine can be performed e.g. by a userwho after termination of the dosing process will initiate the stand-byroutine via a control unit. Preferably, the stand-by routine istriggered automatically. The triggering of the stand-by routinepreferably takes place upon lapse of a predetermined period of timeafter termination of the dosing process. The length of this time periodis preferably from 30 to 60 seconds. By an automated triggering of thestand-by routine, the start of the stand-by routine is advantageouslyindependent from the user and thus cannot be forgotten.

A preferred embodiment of invention will be explained in greater detailhereunder with the reference to the accompanying drawing.

The FIGURE shows a view of a dispensing device for the filling oftitration plates.

In the FIGURE, a device for performing the method of the invention isexemplified by a dispensing device. The dispensing device is connected,by means of a mounting plate 10, to a holding device provided fordisplacement of the dispensing device so that dispensing tips 12 aremovable into positions located above the wells of a titration plate. Thedispensing tips 12 which have a dosing orifice formed therein areconnected to a micropump 14 for dispensing sample liquid from thedispensing tips 12. Each micropump 14 is connected via a tube 16 to asupply container 18. The supply container 18 has sample liquid providedtherein. Further, the micropumps 14 are connected, respectively via atube 20, to a supply container 22 with rinsing liquid.

Each of the micropumps 14 is supported by an adjustment means 24 and isconnected, through the adjustment means 24, to a mounting support 26.Mounting support 26 is fastened to a mounting plate 10.

During a dosing process, sample liquid is pumped by means of themicropumps 14 from the supply container 18 towards the dispensing tips12 and is dispensed in drop-wise fashion via the dosing orifices of thedispensing tips into wells of a titration plate. After dispensing apredetermined number of drops, the dispensing device or the titrationplate will be displaced, and the next wells will be filled.

Once the stand-by routine according to the invention is initiated by theuser or—due to lapse of time—automatically, it is possible that e.g. thefollowing stand-by routine is performed under maintenance of theoperational safety:

Immediately after the initiating of the stand-by routine, a rinsing stepis carried out. In this step, a valve provided on the micropump 14 isswitched by a control unit to the effect that the micropump 14 can suckonly rinsing liquid from the supply container 22 via tube 20. Therinsing process is carried out for a period of about five minutes. Inthe process, liquid is continuously dispensed via dispensing tip 12 intoa receptacle.

After lapse of a period of e.g. 30 seconds upon termination of therinsing process, a droplet dispensing step is performed. The step willlast from about 25 to about 30 milliseconds. During this step, micropump14 is operated with a frequency of about 3500 Hz, causing 100 drops tobe dispensed.

After a further standstill period of about 30 seconds, a further dropletdispensing step is performed which corresponds to the first dropletdispensing step. At intervals of 30 seconds, a predetermined number ofdroplet dispensing steps is performed.

After e.g. 240 droplet dispensing steps, a rinsing step will beperformed again.

These method steps are repeated throughout the stand-by routine. Ifdesired, the time intervals between the individual rinsing steps areshortened, preferably continuously with advancing stand-by time.

For economical reasons, stand-by periods of more than 72 hours arenormally not useful.

1. A method for improving the operational safety of dosing devices forchemical and/or biological liquids, wherein a stand-by routine isinitiated upon termination of a dosing process, the stand-by routinecomprising the following steps: dispensing liquid through a dosingorifice of the dosing device, and repeating the dispensing step after apredetermined period of time.
 2. The method according to claim 1 whereinthe liquid is dispensed in the form of droplets.
 3. The method accordingto claim 1 or 2 wherein, in a liquid dispensing step, a plurality ofdroplets, particularly more than twenty, preferably more than fifty andmost preferably more than eighty, is dispensed.
 4. The method accordingto claim 1 wherein, in a liquid dispensing step, a predeterminedquantity of liquid, particularly from 1 μl to 1 ml, is continuouslydispensed for rinsing the dosing device.
 5. The method according to anyone of claims 1-4 wherein, during a stand-by routine comprising aplurality of liquid dispensing steps, part of the liquid dispensingsteps include a droplet dispensing step and part of the liquiddispensing steps include a rinsing step.
 6. The method according toclaim 5 wherein, between two rinsing steps, a plurality of dropletdispensing steps, preferably more than ten and particularly more thantwenty droplet dispensing steps, are performed.
 7. The method accordingto any one of claims 1-6 wherein the time interval between twosuccessive dispensing steps is from 20 to 80 seconds, particularly from30 to 50 seconds.
 8. The method according to any one of claims 1-7wherein the time interval between two successive dispensing steps isreduced with increased length of the stand-by routine.
 9. The methodaccording to any one of claims 1-8 wherein, in the droplet dispensingstep, sample liquid is dispensed.
 10. The method according to any one ofclaims 1-9 wherein, in the liquid dispensing step, rinsing liquid isdispensed.
 11. The method according to any one of claims 1-10 whereinthe stand-by routine is automatically initiated upon lapse of apredetermined period of time of preferably from 30 to 60 seconds aftertermination of the dosing process.